Clearance line generating system



Feb. 23, 1965 T. L. BEELER ETAL 3,171,120

CLEARANCE LINE GENERATIfiG SYSTEM Filed July 12, 1962 a 3 Sheets-Sheet 1 LINE (CL-2) CLEARANCE SHIP HEADING LINE RIGHT PPI SCOPE E O INVENTORS THEODORE L. BEELER o V LEIGHTON 3. 000/05 0 00 0 2 1 z Z Z ATTORNEY Feb. 23, 1965 T. BEELER ETAL 3,171,120

CLEARANCE LINE GENERATING SYSTEM Filed July 12, 1962 3 Sheets-Sheet 2 United States Patent 3,171,120 CLEARANCE LINE GENERATING SYSTEM Theodore L. Beeler, New Hartford, N.Y., and Leighton B.

Cooke, Winston-Salem, N.C., assiguors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Fiied July 12, 1962, Ser. No. 2110,6438 6 Claims. (Cl. 343) This invention relates to radar equipment and more particularly to electronic circuitry for generating clearance lines to be displayed on a plan position indicator (PPI).

Rarely is it possible or practical to locate shipboard radar-directing and missile-launching equipment in order to have complete 360 azimuth coverage, the reason for this being that a sector in azimuth will be obscured by the ships superstructure. Obviously it is imperative that the missile launcher be clear of the ships superstructure upon firing of the missile. In addition the radar equipment must be provided with an unobstructed azimuth sector throughout the entire flight of the missile to permit complete monitoring of the target and guidance of the missile. In present installations the director and the launcher are displaced one from the other, thus the clearance conditions for each are different. To aggravate the situation each ship will have a plurality of associated launchers and directors. In order to properly evaluate a tactical situation and to ensure the welfare of the ship, these unclear or obscured sectors must be taken into consideration.

It has been found that the most convenient way in which to account for these unclear or obscured sectors is to display them on a plan position indicator. In the past, the equipment was designed to display the unclear sector as the area between two fixed radial lines on the PPI, however no means was provided to vary the angular relationship of these radial clearance lines and thus 'the extent of the obstruction caused by the ships superstructure. As a result the equipment had to be designed not only for a particular ship but for a specific location on that ship based on available clearance information. It has also been found that the extent of obstruction in many cases varies depending upon the elevation of the launcher and the director.

The general purpose of this invention is to provide electronic circuitry for generating clearance lines which overcomes all of the above noted disadvantages inherent in the equipment used heretofore. To attain this, the invention contemplates electronic equipment which can be adjusted on shipboard to accurately display on the PPI scope the clearance conditions of any ship.

An object of the present invention is to provide electronic clearance line generating equipment which can be readily adjusted after shipboard installation to accurately represent clearance conditions of the particular ship.

A further object is to provide means for testing the clearance line generating equipment to determine if the equipment is functioning properly.

Still another object is to provide means for rapidly varying the operation of the equipment after it has been adjusted for specific clearance conditions in order that the actual clearance at a specific elevation of the launching equipment can be more accurately approximated.

A still further object of the invention is to provide means for correlating the clearance lines with an electronically generated ships heading line and to rotate these lines from relative to true coordinates.

With these and other objects in view, as will hereinafter more fully appear, and which will be more particularly pointed out in the appended claims, reference is now made to the following description taken in connection with accompanying drawings in which:

FIG. 1 is a schematic diagram showing a single clearance line generating'circuit;

FIG. 2 is a partial schematic diagram showing the manner in which plural clearance line generating circuits are coupled as contemplated by the instant in- Vention;

FIG. 3 is a block diagram showing the components used to connect the clearance line generating circuits to the PPI scope;

FIG. 4 is an illustration of a typical display as it appears on the PPI scope.

Referring now to FIG. 1 of the drawings there is shown a circuit diagram of a clearance line generating circuit embodying the present invention. Rotary switch It is a motor driven switch which applies deflection voltages and their associated brightening signals to a PPI circuit in correct time sequence. The rotary switch assembly consists of a plurality of switches (decks) which are driven in synchronism .by a constant speed motor (not shown). One of the switch decks is used as a brightening deck (referred to in the specification as Z deck) and two are used for the positioning voltage decks (referred to as X :and Y decks). Operation of the clearance line generating circuit is initiated by rotation of time sharing switch 10 which momentarily grounds the input terminal T1 through resistor 11. An enabling voltage of +l35 volts is applied to the input terminal T1 through resistor 12. The resistors 12 and 13, the latter connecting the input terminal to ground, cooperate to form a voltage divider circuit with the junction therebetween coupled to the grid of amplifier 15 through capacitor 16. Amplifier 15 is biased for conduction by a +135 volt source which is applied to the grid through resistor 17 While the cathode is grounded and the plate is connected to ground through capacitor 18. The output from amplifier 15 is taken from the ungrounded side of capacitor 18 and applied to the grid of amplifier 20 which has a +135 volt source applied to the grid through resistor 21. The cathode of amplifier 20 is grounded through the parallel combination of resistor 22 and capacitor 23 which provides enough bias to maintain the tube only slightly conducting. The plate is connected to a +135 volt supply through the primary of transformer 25. The output from the transformer secondary is applied to a sinecosine potentiometer 30 which is grounded at intermediate points 31 and 32 and has adjustable taps 36 and 37 mounted for rotation on shaft 38. The transformer secondary is shunted by a diode 33 and further includes a feedback path for coupling the output signal through the parallel combination of capacitor 34 and resistor 35 to the grid of amplifier 20.

As the time sharing switch 10 rotates, resistor 11, connected between the switch arm and ground, is periodically connected to the input terminal T1. During periods when this resistor 11 is connected to the input terminal the voltage across resistor 11 will be approximately +60 volts which is used to unblank or brighten the PPI over line 14 during the periods when the clearance line is to be displayed. The voltage at input terminal T1 is also at +60 volts while the switch is closed and, at the end of the switch closure period, instead of dropping to zero as in the case of the brightening pulse, the voltage rises to approximately volts. This negative-going pulse which appears at input terminal T1 is used to start and stop the clearance generator in synchronism with the brightening pulse. The amplitude of these pulses is controlled by the values of resistors 12 and 13, as well as the resistor 11 associated with the time sharing switch. The volt enabling voltage being fed to the top of resistor 12 when clearance line displays are desired and removed when no clearance line displays are desired. Removal of this voltage effectively disables the clearance line generator because it is the source voltage for the brightening and clearance line generator control pulses.

During the periods when no pulse is present, amplifier 15 conducts heavily because its grid is returned to the +135 volt supply through resistor 17 and consequently the voltage at the plate of amplifier 15 is low because of the large drop across resistor 21. When the time sharing switch contact closes, the negative-going pulse produced at input terminal T1 is coupled to the grid of amplifier 15 via capacitor 16 causing the amplifier to be cut off for the duration of the contact closure. When the amplifier is cut off the plate voltage tends to rise rapidly but the charging current required by capacitor 18 causes the voltage to rise exponentially. This exponential rise continues until the end of the pulse whereupon amplifier 15 again conducts heavily and discharges capacitor 18. Thus the voltage at the plate of amplifier 15 is a positive-going sawtooth pulse lasting for the duration of the brightening pulse. This pulse has the desired wave shape to generate the clearance line but must be amplified to produce a line of the required length.

The sawtooth pulse voltage appearing at the plate of amplifier 15 is fed directly to the grid of amplifier 21) where it is amplified and then applied to the sine-cosine potentiometer 30 via transformer 25. Resistor 22 coupled to the cathode of amplifier 21 provides sufficient bias to keep this amplifier almost cut off between pulses and the charge developed in capacitor 23 maintains this bias during the pulse interval. Capacitor 34 and resistor 35 provide negative feedback to improve the sawtooth voltage linearity while diode 33 in the secondary of transformer 25 eliminates the transients that would otherwise occur at the end of the sawtooth voltage due to the inductance of the transformer.

The sawtooth voltage appearing across the transformer primary has an amplitude of approximately 24 volts and with a turns ratio of 1:1 in the transformer the amplitude of the secondary voltage is also approximately 24 volts. Since the secondary is effectively center-tapped by the sine-cosine potentiometer 31), the voltages applied to each half of the potentiometer have an amplitude of i 12 volts. The potentiometer has two outputs, hereafter referred to as X and Y, taken from adjustable taps 36 and 37, one of these voltages is proportional to the sine of the potentiometer shaft angle and the other proportional to the cosine of the shaft angle. Since the applied voltages have an amplitude of 12 volts, the amplitudes of the two output voltages are 12 times the sine of the shaft angle and 12 times the cosine of the shaft angle. Rotation of the sine-cosine potentiometer shaft 38 causes the amplitudes of the outputs X and Y to vary in such a manner that when applied to the deflection plates of the PPI the length of the clearance line remains constant while the angular orientation of the line varies in accordance with the potentiometer setting.

FIGURE 2 shows the application of this circuit for generation of both the right and the left clearance lines. In order to make the clearance line displays more accurately represent the actual blind-zones, provisions have been made to display either a wide, narrow, or no blindzone for each weapon and the associated fire control systems. The type of display chosen is a function of the weapon elevation angle at the time of firing. Selection of the display is made by switches 40 and 41 in the fire control center, which control relays 42 and 43 in the clearance line generator circuits as shown in FIGURE 2. Each line generator drives two sine-cosine potentiometers connected in parallel, one for the wide blind-zone display and the other for the narrow blind-zone display. Relay 43 is operated to connect the wide blind-zone potentiometers t and 50' to the output leads and relay 42 is 4 operated to connect the narrow blind-zone potentiometers 3t) and 39' to the output leads.

When neither relay is operated, the output leads are grounded through the back contacts of relay 42 to eliminate interference. Additional contacts on relays 42 and 43 remove the enabling voltage from the line generators when neither relay is operated to prevent the generation of brightening spots which would cause an undesirable bright spot in the center of the cathode ray tube during the no blind-zone condition.

The TEST relay 51 is used, in conjunction with TEST switch 52 to test the clearance line generator circuits. When relay contacts 53 are operated, the external leads form the fire control system are disconnected and the coil leads of relays 42 and 43 are transferred to the TEST switch 52 which may then be used to obtain either a wide or narrow type display. This relay 51 may be operated by switch 54 provided on the Master Control Panel.

As will be understood from the description to follow the circuit of FIG. 1 is capable of generating a single radial line on the PPI scope and in order to generate the second radial line and thereby define the boundaries of the blind-zone on the scope a second circuit identical to FIG. 1 must be used. This arrangement is shown in FIG. 2 of the drawings where like parts are designated by like reference numerals and corresponding parts are designated by primed reference numerals.

Terminals T1 and T2 are connected to individual poles of the time sharing switch 10, shown in FIGS. 1 and 3, to be sequentially grounded through resistor 11 whereby generation of a clearance line by the circuit of FIG. 1 is initiated and a brightening pulse is developed on line 14 to unblank the PPI scope. The enabling voltage is selectively applied to the clearance line generator circuits, which are shown in block form and are identical to the circuit of FIG. 1, over relay contacts 69 and 61 which are controlled by relays 42 and 43, respectively. The sinecosine potentiometers shown as 30 and 30' in FIG. 2 correspond to the potentiometer 30 shown in FIG. 1. In order to vary the angular relationship of the clearance lines once adjustment of the taps on potentiometers 3t and 30 have been made a second pair of sine-cosine potentiometers 50 and 56 are connected in parallel with the first pair. With the taps of the second pair of potentiometers adjusted to a different setting, rapid switching from a narrow blind-zone to a wide blind-zone PPI display may be effected. Switching from the wide blind-zone to the narrow blind-zone is accomplished by selective operation of relays 42 and 43 which control ganged relay contacts to effectively connect either the first pair or the second pair of potentiometer taps to the output circuit. Energization of these relays is controlled by the selective operation of switches 40 and 41 which may be located in the fire control center. The clearance line generators may be tested upon closure of switch 54 which may be located in the master control panel to energize test relay 51 which operates to disconnect the relays 42 and 43 from the fire control center and renders switch 52 operative to selectively energizing relays 42 and 43 for wide and narrow zone operation.

Turning now to FIG. 3 there is shown the manner in which the clearance line generators of FIGS. 1 and 2 are connected to the PPI scope for portrayal of the blind or obscured zones. The X and Y outputs designated CL1 and CL-Z from the clearance line generators are coupled to amplifiers 72 and 73, respectively, by way of input network 70 which may take the form of a conventional diode OR network.

The ships heading generator circuit 71 generates the ships heading waveform voltage. The circuit receives a pulse from a voltage input that represents the ships heading. This voltage comes through the time-sharing switch 10 through the Z deck. As switch 10 rotates, closure of a contact on the Z deck triggers the ships heading generator 71 and this triggering pulse causes a pulse voltage, which corresponds to the ships heading line, to appear at the input to the Y resolver driving amplifier. During the time period when the ships heading generator circuit is enabled, the voltage is passed to the ship heading and clearance line resolver 74 as a brightening voltage for the ships heading line. The output of the clearance line resolver connects the voltage through amplifier 77 and a switch contact on the Y deck of switch to place this voltage on the PPI in proper time sequence with the brightening voltages of the X and Y components from the two clearance line generator circuits as shown in FIG. 2.

The outputs of amplifiers 73 and72 are fed to clearance line resolver 74 which'is driven by the ship heading servo 75 which converts the clearance line signals and the ship heading signals from relative bearings to true bearings. The output from the resolver 74 is fed to amplifiers 76 and 77 for presentation to the X78 and Y79 decks of time sharing switch 10. The outputs from the X78 and Y79 decks of time sharing switch 10 are fed to the deflection plates of the PPI scope for sequential presentation of first the left clearance line, then the ship heading line and finally the right clearance line, under control of the Z deck, shown in more detail in FIG. 1.

A typical display as it appears on the PPI scope is shown in FIG. 4 wherein the sector, in which is contained the ship heading line, represents the blind or unclear Zone due to the ships superstructure. It will be noted in this illustration that the ship heading line bisects the angle between the right and left clearance line. This represents the usual situation where the launcher and director is situated somewhere along the center line of the ship and thus the ships superstructure would offer equal obstructions on both sides of the ship heading line.

In light of the foregoing description, the overall operation of the invention is believed obvious. Each of the circuits of FIG. 1 operates to generate a single clearance line by connecting the X and Y sawtooth functions taken from the sine-cosine potentiometers to the PPI scope as shown in FIG. 3. The ship heading generator 71 generates a sawtooth function which is interposed in time between the generation of the left clearance line and the right clearance line as controlled by the time sharing switch 10. The resolver 74, which is basically a synchro, under the control of the ship heading servo 75 functions to modify the X and Y components of the input signals such that the ship heading line as portrayed on the PPI scope correctly indicates the actual bearing of the ship with the clearance lines positioned in correct angular relationship thereto.

Obviously, additional pairs of clearance lines generating circuits under the control of time sharing switch 10 could A be connected to the input network 70 to indicate the clear ance conditions at various shipboard locations on the same PPI scope.

While there has been described a preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention as defined by the appended claims.

What is claimed is:

1. A system for displaying the degree of obstruction to shipboard weapons systems offered by the ships superstructure on a PPI scope as the region bounded by two radial clearance lines comprising a time sharing switch having open and closed positions; first and second like clearance line generating circuits sequentially energized by closure of said time sharing switch; said clearance line generating circuits each including means for developing and amplifying a sawtooth voltage function only when energized by closure of said time sharing switch, a transformer having a primary for receiving said sawtooth voltage function and a secondary, and a sine-cosine potentiometer connected across said transformer secondary with adjustable taps for converting said sawtooth voltage function into sine and cosine output signal components; a ship heading generator responsive to closure of said'time sharing switch for generating a second sawtooth voltage function; a resolver controlled by a ship heading servo and responsive to the output signals of said ship heading generator and each of said clearance line generating circuits for converting said signals from relative to true bearing coordinates; and a PPI scope responsive to the outputs from said resolver and controlled by closure of said time sharing switch for displaying said clearance lines and a ship heading line in consecutive fashion.

2. A system for displaying the degree of obstruction to shipboard weapons systems offered by the ships superstructure on a PPI scope as the region bounded by two radial clearance lines comprising a time sharing switch, first and second like clearance line generating circuits actuated by said time sharing switch in alternate fashion to produce output signals for generating a radial clearance line on said PPI scope, adjusting means included Within each of said clearance line generating circuits to permit variation of said output signals and corresponding adjustment of the bearing angle of said radial clearance line displayed on said PPI scope, a ship heading generator circuit for providing voltage output which is proportional to the ships heading, and a resolver controlled by a ship heading servo for coupling the outputs of each of said clearance line generating circuits and said ship heading generator to said PPI scope whereby the clearance conditions displayed on said PPI scope are correlated with the bearing of the ships heading.

3. A system for displaying the degree of obstruction to shipboard weapons systems offered by the ships superstructure on a PPI scope as the region bounded by two radial clearance lines comprising a time sharing switch having open and closed positions; first and second clearance line generating circuits sequentially and periodically activated by said time sharing switch; each of said first and second line generating circuits including means connected to said time sharing switch for periodically developing a sawtooth voltage pulse, a transformer having a primary energized by said sawtooth voltage pulse and a secondary, first and second parallel sine-cosine potentiometers connected across said secondary, each of said first and second sine-cosine otentiometers having a pair of adjustable taps for converting said sawtooth voltage pulse into different sine and cosine component signals; a PPI scope connected to each of said first and second clearance line generating circuits and responsive to said sine and cosine signal components for displaying two angularly space radial clearance lines; and relay switching means selectively operable to connect said pair of adjustable taps of either said first sine-cosine potentiometer or said second sine-cosine potentiometer of each of said clearance line generating circuits to said PPI scope.

4. A clearance line generating circuit for displaying lines on a PPI scope that represent the clearance conditions of a weapon comprising a first amplifier circuit having an input and an output; an enabling voltage source coupled to the input of said first amplifier; said enabling voltage delivering a voltage pulse to the input of said first amplifier periodically by a switching means for providing said first amplifier to be cut-off for the duration of the switch closure and to conduct upon switch opening; a capacitor connected to said output of said first amplifier for providing a sawtooth voltage pulse; a second amplifier having an input and an output; said second amplifier receiving the sawtooth voltage at its input; a transformer means having primary and secondary windings with said primary winding connected for receiving the output of said second amplifier; feedback network means coupled to one side of said secondary winding for providing a feedback voltage to the input of said second amplifier to improve amplifier operation; and a sine-cosine potentiometer coupled across said, secondary winding for providing two output voltages, one which is propor- 7 tional to the sine function of [the input voltage and the other which is proportional to the cosine function.

5. A system for displaying the degree of obstruction to shipboard weapons systems offered by the ships superstructure on a PPI scope as the region bound by two radial clearance lines comprising a time-sharing switch having open and closed positions; first and second line generating circuits sequentially and periodically activated by closure of said time-sharing switch; each of said line generating circuits including means for developing and amplifying a saw-tooth voltage function only when energized by closure of said time-sharing switch; a sine-cosine potentiometer coupled to receive the sawtooth voltage for converting said sawtooth voltage into sine and cosine signal components; and a PPI scope coupled to display said sine-cosine sign-a1 components.

6. The system as claimed in claim 5 wherein said first and second line generating circuits include a first amplifier circuit having an input and an output; pulse voltage source means coupled to the input of said first amplifier; said pulse voltage source means delivering a voltage pulse to the input of said first amplifier periodically by a switching means for providing said first amplifier to be cut-01f for the duration of the switch closure and to conduct upon switch opening; a capacitor connected to said output of said first amplifier for providing a sawtooth voltage pulse; second amplifier having an input and an output; said second amplifier receiving the sawtooth voltage at its input; transformer means having a primary and secondary winding with said primary winding connected for receiving the output of said second amplifier; and said secondary coupled to said sine-cosine potentiometer.

References Cited by the Examiner UNITED STATES PATENTS 2,567,862 9/51 Van Voorhis 3436 2,801,366 7/57 Janssen et al. 315--29 X 2,820,894 1/58 Schrecongost 31529 X 2,858,531 10/58 Stocker 3435 3,005,928 10/61 Wuster 31529 X CHESTER L. JUSTUS, Primary Examiner. 

4. A CLEARANCE LINE GENERATING CIRCUIT FOR DISPLAYING LINES ON A PPI SCOPE THAT REPRESENT THE CLEARANCE CONDITIONS OF A WEAPON COMPRISING A FIRST AMPLIFIER CIRCUIT HAVING AN INPUT AND AN OUTPUT; AN ENABLING VOLTAGE SOURCE COUPLED TO THE INPUT OF SAID FIRST AMPLIFIER; SAID ENABLING VOLTAGE DELIVERING A VOLTAGE PULSE TO THE INPUT OF SAID FIRST AMPLIFIER PERIODICALLY BY A SWITCHING MEANS FOR PROVIDING SAID FIRST AMPLIFIER TO BE CUT-OFF FOR THE DURATION OF THE SWITCH CLOSURE AND TO CONDUCT UPON SWITCH OPENING; A CAPACITOR CONNECTED TO SAID OUTPUT OF SAID FIRST AMPLIFIER FOR PROVIDING A SAWTOOTH VOLTAGE PULSE; A SECOND AMPLIFIER HAVING AN INPUT AND AN OUTPUT; SAID SECOND AMPLIFIER RECEIVING THE SAWTOOTH VOLTAGE AT ITS INPUT; A TRANSFORMER MEANS HAVING PRIMARY AND SECONDARY WINDINGS WITH SAID PRIMARY WINDING CONNECTED FOR RECEIVING THE OUTPUT OF SAID SECOND AMPLIFIER; FEEDBACK NETWORK MEANS COUPLED TO ONE SIDE OF SAID SECONDARY WINDING FOR PROVIDING A FEEDBACK VOLTAGE TO THE INPUT OF SAID SECOND AMPLIFIER TO IMPROVE AMPLIFIER OPERATION; AND A SINE-COSINE POTENTIOMETER COUPLED ACROSS SAID SECONDARY WINDING FOR PROVIDING TWO OUTPUT VOLTAGES, ONE WHICH IS PROPORTIONAL TO THE SINE FUNCTION OF THE INPUT VOLTAGE AND THE OTHER WHICH IS PROPORTIONAL TO THE COSINE FUNCTION.
 5. A SYSTEM FOR DISPLAYING THE DEGREE OF OBSTRUCTION TO SHIPBOARD WEAPONS SYSTEMS OFFERED BY THE SHIP''S SUPERSTRUCTURE ON A PPI SCOPE AS THE REGION BOUND BY TWO RADIAL CLEARANCE LINES COMPRISING A TIME-SHARING SWITCH HAVING OPEN AND CLOSED POSITIONS; FIRST AND SECOND LINE GENERATING CIRCUITS SEQUENTIALLY AND PERIODICALLY ACTIVATED BY CLOSURE OF SAID TIME-SHARING SWITCH; EACH OF SAID LINE GENERATING CIRCUITS INCLUDING MEANS FOR DEVELOPING AND AMPLIFYING A SAW-TOOTH VOLTAGE FUNCTION ONLY WHEN ENERGIZED BY CLOSURE OF SAID TIME-SHARING SWITCH; A SINE-COSINE POTENTIOMETER COUPLED TO RECEIVE THE SAWTOOTH VOLTAGE FOR CONVERTING SAID SAWTOOTH VOLTAGE INTO SINE AND COSINE SIGNAL COMPONENTS; AND A PPI SCOPE COUPLED TO DISPLAY SAID SINE-COSINE SIGNAL COMPONENTS. 